Treatment of cast iron



Patented June 29, 1948 TREATMENT OF. CAST IRON Harry B. Kinnear, Columbus, Ohio, assignor, by mesne assignments, to Chromium Mining &

Smelting Marie, Canada Corporation, Ontario, Canada, a corporation of Limited, Sault Ste.

No Drawing. Application October 5, 1945, Serial No. 620,651

6 Claims. (01. 75-130) This invention relates to metallurgy and has for an object the provision of certain improvements in metallurgical methods or processes. More particularly, the invention contemplates the provision of certain improvements in methods or processes suitable for use in the production of cast iron. A particular object of the invention is to provide an improved method or process for improving the mechanical or physical properties of cast iron. A specific object of the invention is to provide an improved method or process for producing high-strength cast iron. A further object of the invention is to provide an improved process for utilizing exothermic reaction mixtures in the production of high strength cast iron.

The invention is based on my discovery that cast iron can be treated while in the molten state with an exothermic reaction mixture comprising silicon, strontium and a nitrate radical to produce cast iron products having improved mechanical or physical properties. Thus, for example, I have found that by reacting with such a reaction mixture molten cast iron, such as cupola iron and blast furnace iron, containing about two and seventy-five hundredths percent (2.75%) to three and twenty-five hundredths percent (3.25%) of carbonand silicon in amount less than that required for high-strength cast iron; cast iron products having improved transverse, tensile, deflection, impact, hardness and other properties can be produced. Thus, for example, exothermic reaction mixtures may be employed in accordance with the method or process of invention to convert cast iron products of the above-indicated compositions with respect to carbon and silicon and having tensile strengths ranging from about 30,000 to 35,000 pounds per square inch to cast iron products having tensile strengths in the range, 40,000 to 55,000 pounds per square inch. The method or process of the invention is particularly useful for producing gray cast iron. I

The depth of chill of cast iron treated with exothermic reaction mixtures in accordance with the invention is not materially difierent from that of an untreated cast iron of equivalent silicon and carbon contents.

In carrying out a method or process of the invention, molten cast iron from any suitable source is reacted in a ladle, for example, with an exothermic reaction mixture in amount sufiicient to modify the mechanical or physical properties or characteristics of the cast iron by increasing the silicon content without altering substantially the composition of the cast iron with respect to total carbon.

In carrying out a method or process? of the invention, I may employ an exothermic reaction mixture comprising a nitrate of any metal of the group consisting of strontium, barium, calcium and magnesium, or I may employ an exothermic reaction mixture comprisin a compound of strontium, a nitrate of another metal and silicon. Two or more nitratesmay be employed in a reaction mixture if desired. Sodium nitrate may be employed in conjunction with any one or more of the nitrates of strontium, barium, calcium and magnesium. 1

Exothermic reaction, mixtures employed in carrying out a method or process of the invention preferably contain ferrosilicon as the source of silicon, and they preferabl are formed by grinding together the components to form mixtures of particles most or all of which are small enough to pass a 100-mesh screen. Grinding together of the components results in thorough and intimate mixing which is conducive to efiective and complete reaction. The reaction mixtures may be employed in the form of loose powders or inthe form of agglomerates or briquets. Any suitable bonding agent may be employed in forming theagglomerates or briquets. When sodium nitrate is employed, it may function as the bonding agent. Thus, for example, a finely divided mixture comprising sodium nitrate may be moistened with water in amount by weight equal to about two to three percent (2 to 3%) of theweight of the mixture, molded, heated to drive off water and melt the sodium nitrate and cooledto permit solidificae tion of the sodium nitrate in place. The solidified sodium nitrate is intimately associated with the other components and functions as the bonding agent. r

The components of a reaction mixture employed in carrying out a method or process of the invention are so proportioned as to providesilicon in excess of the amount which can be oxi-v diz'ed by all of the nitrate and any other reducible compound which may be present. The excess silicon enters the molten cast iron, increasing the silicon concentration and causing a graphitizing eifect on the carbon contained therein. Nitrate and silicon for oxidation by the nitrate preferably are employed in amounts such that, by reaction, suflicient heat is generated to melt the 50.

Ferrosilicon (75% Si) 8 1 Ferrosilicon (50% Si) 16 Strontium nitrate-SflNOzh 22.5 Sodium nitrate-NaNOz 2.5 Sodium silicate .62

Ferrosilicon (75% Si) 83.4 Strontium nitrate-Sr(NO3)-2 16.6

III

Ferrosilicon (75% Si) 81.7 Strontium nitrate-Sr (N03): 18.3

Ferr sili on 5% T--- Strontium nitrate- Sr(N03)2 18.0 Sil ca fl ur.- 2.0

Ferrosilicon (75% Si) 82.4 Sodium nitrate-NaNoa 5.1 Strontium nitrate- Sr(NO3)2 12.5

Ferrosilicon (75% Si) 80.0 Barium nitrate-Ba(NOc)2 20.0

Ferrosilicon (75% Si) 100.0 Strontium nitrateeSr(NO3)2 22.5

VIII

Ferrosilicon (75% Si) 100.0 Strontium nitrate-Sr(NOs)2 22.5 Sodium nitrate-NaNOe 25 EerrosilicQ f (58.75% Si).. 2 100.0 Strontium mtratc-Sr(NO3) 22.5

c o ccn 5% Si) 100-0 Strontium nitrate-.Sr(NO3)z 14.6 Sodiu it te-lI B -M 4-,. 2.

Ferrosilicon (75% Si) or '100.0 Strontium nitrateesflNOfl-e 8.9

Sodium nitrate-NaNOs 2.1

The following examples illustrate results obtained in treating molten cast iron products with exothermic reaction mixtures of the types illustrated above in accordance with the method or process of the invention (the exothermic reaction mixtures were added to molten cast iron in hand ladles each containing sixty pounds of cast iron, and the metal was stirred Well before testbarcastings were poured). XII

Chemical Analysis Mechanical Properties Mixture Added g rans-v e cc cnm- 0 M n S1 verse tion 'sile' pact Example VII. 2. 09 .78 1. 2 3, 370 .311 51, 000 51. 0 Example VIIL 3. 03 82 1. 26 3, 560 333 50, 000 60. 3 Example 3. 02 .74 1. a2 3, 3.40 .273 43, 800 54. 2 Example X.-- 3. 08 .83 1. ll 3, 510 320 53, 500 56. 8 Example XL... 3. 08 .83 1. 23 3, 460 345 ,800 61. 8

' The base iron used in the tests in which the results set forth abovewere obtained was a lowsilicon (.70 to .80% Si) cupola cast iron normally made according to standard commercial cupola 3 or the reaction mixture being of such composi tions and being present in such proportions as to be capable of reacting exothermically upon contact with the molten cast iron to decompose the nitrate radical, oxidize a portion only of the silicon and melt and incorporate'in the molten cast iron the remainder of the silicon.

2. The method of producing high-strength cast iron which comprises contacting molten cast iron containing silicon in an amount less than that required for high-strength cast iron with an exothermic reaction mixture comprising silicon, strontium and one or more nitrates of the group consisting of calcium, strontium, barium and magnesium, the components of the reaction mixt e n f su h com os ion an ng ent n such pr orti s a o b p ble f eac ng exothermically upon contact with the molten cast iron to decompose the one or more nitrates, oxidize a portion only of the silicon and melt and incorporate in the molten cast iron the remainder of th s licon.

3. The method of producing high-strength cast iron which comprises contacting molten cast iron containing silicon in an amount less than that required for high-strength cast iron with an exothermic reaction mixture comprising silicon and strontium nitrate, the components of the reaction mixture being 0f such compositions and being present in such'p'roportions as to be capable of reacting exothermically upon contact with the molten cast iron to decompose the strontium nitrate, oxidize a portion only Of the silicon and melt and incorporate in the molten cast iron the remainder of the silicon.

4. The method of producing high-strength cast iron which comprises contacting molten cast iron containing silicon in an amount less than that required for high-strength cast iron with an exo thermic reaction mixture comprising ferrosilicon, sodium nitrate and strontium nitrate, the components of the reaction mixture being of such compositions and being present in such proportions as to be capable of'reacting exothermically upon contact with the molten cast iron to decompose the sodium and strontium nitrates, oxidize a portion only of the ferrosilicon andmelt and incorporatein the molten cast iron the remainder of the ferrosilicon,

' 5. The method of producing high-strength cast iron which comprises contacting molten cast iron containing carbon in the range two and seventyfive one-hundredths percent (2.75%) to three and twenty-five one-hundredths percent (3.25%) by weight and containing silicon in an amount less than that required for high-strength cast iron with an exothermic reaction mixture comprising silicon, strontium and a nitrate radical, the components of the reaction mixture being of such compositions and being present in such proportions as to be capable of reacting exothermically upon contact with the molten cast iron to decompose the nitrate radical, oxidize a portion only of the silicon and melt and incorporate in the molten cast iron the remainder of the silicon.

6. The method of producing high-strength cast iron which comprises contacting molten cast iron containing carbon in the range two and seventyfive one-hundredths percent (2.75%) to three and and twenty-five one-hundredths percent (3.25%) by Weight and containing silicon in an amount less than that required for high-strength cast iron with an exothermic reaction mixture comprising silicon and strontium nitrate, the

HARRY B. KINNEAR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,154,613 Guthrie Apr, 18, 1939 2,243,783 Udy May 27, 1941 2,280,872 Udy Apr. 28, 1942 OTHER REFERENCES The Foundry, January 1938, article entitled: Late Silicon Additions to Cast Iron, by Crosby and Herzig. On file in Div. 3. -130. 

